Time and Task Dependencies

PERT (Performance Evaluation and Review Technique) charts primarily show how the different tasks are connected by presenting these as a network of boxes (activities) linked with lines. Due to a lack of a common time scale, start and finish dates have to be added to each individual task box. Complex PERT charts are difficult to survey and are less suitable for presentation purposes of the entire project. However, they are commonly used during the establishment of a project plan and to illustrate dependencies within a selected part of the project, because they expose the logic of a project. 

Linked Gantt charts visualize both key elements, task duration and dependency, by superimposing the task links as connecting lines on a Gantt chart. If complex dependencies exist, the plan loses its clarity or can become totally confused. This can be avoided by graphic means (line thickness, use of colours) or by indicating only those links which are critical and not obvious. 

In the example, the achievement of objectives 1/2 (70% purity) and 1/3 (immunoreactive in vitro) could be used as milestones which successfully conclude the antigen preparation phase. However, the definition immunoreactivity in vitro seems too inexact for use as a milestone. A better and adequate specification could be for example immunoreactive with monoclonal antibody Y , whereby antibody Y is directed against the most relevant epitope of Antigen X. 

Phase II of the project example contains an objective describing the desired type and specificity of the B-cell response ( II/2) and it is specific enough in its definition (neutralization of the twofold challenge dose) to serve as a meaningful milestone - provided that the project team agrees on its usefulness at that place. 

As described above, the backbone of the plan is basically established starting at the end of the project, then working through to the beginning. To sequence the different task sections correctly it is necessary to check backwards and forward to see how the different tasks depend on each other. 

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